This application claims priority to German Patent Application No. 102 15 018.4, which is hereby incorporated by reference herein.
The present invention relates to a DC electromagnet made of sheet metal magnet parts for use in an electric switchgear, in particular in a contactor having a driving coil.
There are DC electromagnets, used in contactors in particular, in various forms. If such electromagnets include two pairs of pole faces, for example, with a U-shaped magnet yoke having a rod-shaped armature which closes the magnet yoke or with E-shaped magnet parts, the relative positions of the pole face pairs must be adjusted. Furthermore, such electromagnets have at least two working air gaps which partly determine the power loss.
German Patent No. 35 05 724 C2 and U.S. Pat. No. 4,700,165 describe systems having an E-shaped fixed magnet core and an E-shaped movable magnet core. There are three pairs of pole faces and three working air gaps. The straight-line relative motion of the magnet cores with respect to each other without tipping must be ensured using guide devices. In particular, the ends of the lateral legs of the magnet cores are provided with angled surfaces resulting in self-alignment.
A similar system having E-shaped fixed and movable magnet cores is known from German Patent Application No. 28 44 361 A1. Also in this system the ends of the lateral legs of the magnet cores are angled and guide devices are used to stabilize the relative motion of the magnet cores with respect to each other.
An object of the present invention is to provide a DC electromagnet having a comparable power loss and functionality, reduced manufacturing costs, and the fewest possible number of magnet parts and a reduced number of pole face pairs.
The present invention provides a DC electromagnet system made of sheet metal magnet parts for use in an electrical switchgear, in particular in a contactor having a driving coil. The system comprises a fixed magnet yoke (10) formed by a central web (12) and two legs (11). The free ends (14, 14xe2x80x2) of the magnet yoke legs (11) are situated spaced from one another forming a narrow passage (23) for a movable, prismatic armature (60). The armature (60) is guided in its displacement stroke by guide devices (40), the free ends (64) of the armature (60) being directed toward the central web (12) of the magnet yoke (10). A working air gap (22) is formed between the free end (64) of the armature (60) and the center of the central web (12), perpendicular to the longitudinal axis of the armature (60), the faces of the armature being inclined at an angle to the axis of the armature (60).
The present invention uses no E-shaped magnet bodies. In contrast with the above-named related art, there is only one working air gap.
Thus, according to the present invention, the fixed magnet yoke is designed in a ring shape or a C shape and includes a central web and two magnet yoke legs forming an angle with the central web. Furthermore, a single working air gap is formed between the free end of the movable prismatic armature and the center of the central web, perpendicular to the longitudinal axis of the armature; the two free leg ends of the magnet yoke extend to the proximity of the armature, where a narrow passage is formed for the armature.
In its displacement stroke, the armature is guided by guide devices. The free end of the armature is directed toward the central web of the magnet yoke and the faces of the working air gap are designed to form an angle with the armature""s axis.
The narrow passage formed between the free ends of the magnet yoke legs and the armature represents another parasitic air gap, whose magnetic resistance does not change during displacement stroke movements.
A symmetrical design of the working air gap is preferred, in which the faces are wedge-shaped. The wedge shape of the working air gap is designed at the free end of the armature so that the wedge tip is in the plane of symmetry of the central web and the wedge is oriented toward the central web. Correspondingly, the wedge shape of the working air gap on the central web is designed as a wedge-shaped recess. The working air gap is provided with at least one stop made of non-magnetic material, the material forming the remanent air gap when the magnetic circuit is closed.
With the design of symmetrical, wedge-shaped faces in the working air gap, well-defined force relationships between armature and magnet yoke are achieved. No sideward tipping or slipping may occur on the angled surfaces, since a kind of self-centering takes place. With the wedge-shaped design, the effective magnetic surface and thus the magnetic energy in the air gap is intensified, in particular when the air gap is large.
In the following, xe2x80x9cyoke profilexe2x80x9d will be understood as the inner space formed by the inner surfaces of the lateral legs and of the central web. The face of the central web facing the yoke profile may be preferably designed without elevations or projections into the yoke profile. As an alternative, an extension web, which carries the wedge-shaped recess corresponding to the working air gap formed on the end of the armature, is designed on the central web of the magnet yoke.
An advantage of the above-described magnet system is that, compared to systems having a comparable drive volume and a comparable power loss, higher contact pressure forces are achievable. Furthermore, it is advantageous that the structure is made of stamped stacked metal sheets which may be welded or riveted. The drive may be easily assembled, because only few coupling elements are needed due to the symmetrical structure of the magnet system. The overall manufacturing costs are reduced.
In one of the embodiments, a free space that is as large as possible is created for the assembly of the driving coil. The design of the working air gap takes this requirement (first embodiment) into account in that the entire inner surface of the cross leg facing the magnet armature forms a single plane which has no material formations (elevations) protruding into the yoke profile, which might make the insertion of the driving coil difficult.
Embodiments of the present invention may differ by the length of the armature used and/or the position of the working air gap with respect to the central web of the magnet yoke.